The downsides of the 328 to the 335...
-Less power, the 335 traps about 3-4mph faster and is half a second faster to 60 and in the 1/4
Upsides to the 328...
-A bit lighter on it's feet, a bit more tossable as it's 150lbs or so lighter
-Real world MPG, I drove an 8spd auto 335 on a loop where I got 35.5mpg compared to my 6mt 328 at 39.9. If the 335 was a 6mt, it would have likely been worse.
-Price difference of about $4k, a bit less if both cars are equipped identically.
So to me, the first two things against the 328 were easy to overcome. A proper sounding exhaust worked wonders. Is it the same as a BMW straight 6? No. But it sounds good.
The less power? Easy fix. I got my BMS tune for $300. Look at what it does to the numbers, now every bit as fast or faster than a 355. My exhaust put down an extra 20ft lbs to the wheels and 7whp, so add that to the results below.
So for very little money you have the lighter weight, improved handling and better MPGs out of the 328 with the same or more power of the 355 with improved sound, albeit not the same kind of sound.
I cheated a bit because my exhaust was free and I chose the 328 because of the deal I got and it's the DD to my blown straight 6 BMW-the 335 would have been redundant a bit.